Adaptation of equalizer settings using error signals sampled at several different phases

ABSTRACT

An apparatus includes an error sample generating circuit and an adaptation circuit. The error sample generating circuit is generally configured to generate error samples at a plurality of phases. The adaptation circuit may be configured to adjust one or more equalizer settings based upon a data sample and the error samples.

FIELD OF THE INVENTION

The invention relates to communications generally and, moreparticularly, to a method and/or apparatus for implementing adaptationof equalizer settings using error signals sampled at several differentphases.

BACKGROUND OF THE INVENTION

In communications systems, vertical and horizontal eye margins of asampled signal are measures of system performance. The vertical eyemargin at the desired sampling point should be as large as possible,such that the sampled data is the same as the original data transmitted,even with the presence of latch offset and latch sensitivity. Jitter cancause the actual sampling point to move away from the desired samplingpoint momentarily. The vertical eye margin at the actual sampling pointis what really matters. However, the vertical eye margin at the actualsampling point varies with the sampling point. Instead, the horizontaleye margin is used. The horizontal eye margin measures the range of thesampling phases within which the vertical eye margin is above apredefined threshold. The predefined threshold defines the point beyondwhich the error is eliminated or minimized.

It would be desirable to implement adaptation of equalizer settingsusing error signals sampled at several different phases.

SUMMARY

The invention concerns an apparatus including an error sample generatingcircuit and an adaptation circuit. The error sample generating circuitis generally configured to generate error samples at a plurality ofphases. The adaptation circuit may be configured to adjust one or moreequalizer settings based upon a data sample and the error samples.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be apparent from the followingdetailed description and the appended claims and drawings in which:

FIG. 1 is a diagram illustrating a communication system including areceiver in which embodiments of the invention may be implemented;

FIG. 2 is a diagram illustrating relationships between phases of asampling clock signal and a data sampling eye in a full rate (or 1T)architecture;

FIG. 3 is a diagram illustrating relationships between phases of asampling clock signal and a data sampling eye in a half rate (or 2T)architecture;

FIG. 4 is a diagram illustrating a receiver circuit including a varietyof features in accordance with embodiments of the invention;

FIG. 5 is a diagram illustrating another receiver circuit including avariety of features in accordance with embodiments of the invention;

FIG. 6 is a block diagram illustrating an example implementation of anerror sample generating circuit of FIGS. 4 and 5 in accordance with anembodiment of the invention;

FIG. 7 is a block diagram illustrating another example implementation ofthe error sample generating circuit of FIGS. 4 and 5 in accordance withan embodiment of the invention;

FIG. 8 is a block diagram illustrating still another exampleimplementation of the error sample generating circuit of FIGS. 4 and 5in accordance with an embodiment of the invention;

FIG. 9 is a block diagram illustrating an example implementation of theadaptation circuit of FIGS. 4 and 5 in accordance with an embodiment ofthe invention;

FIG. 10 is a block diagram illustrating another example implementationof the adaptation circuit of FIGS. 4 and 5 in accordance with anembodiment of the invention;

FIG. 11 is a block diagram illustrating still another exampleimplementation of the adaptation circuit of FIGS. 4 and 5 in accordancewith an embodiment of the invention;

FIG. 12 is a diagram illustrating an error sample generating circuit anda bang-bang clock data recovery (CDR) circuit configured to generate aphase adjustment signal in accordance with an embodiment of theinvention;

FIG. 13 is a diagram illustrating an example circuit implementing a halfrate (or 2T) architecture decision feedback equalizer (DFE) and anadaptation circuit using error signals generated at a plurality ofphases in accordance with an embodiment of the invention;

FIG. 14 is a diagram illustrating another example circuit implementing ahalf rate (or 2T) architecture decision feedback equalizer (DFE) and anadaptation circuit using error signals generated at a plurality ofphases in accordance with another embodiment of the invention;

FIG. 15 is a diagram illustrating still another circuit implementingbang-bang phase detector (PD) along with a half rate (or 2T)architecture decision feedback equalizer (DFE), and generating errorsignals sampled at a plurality of phases in accordance with anembodiment of the invention;

FIG. 16 is a flow diagram illustrating a process for adapting parametersof one or more equalizers in a receiver based upon error signals sampledat several different phases in accordance with an embodiment of theinvention;

FIG. 17, is a diagram illustrating a DFE feedback waveform.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention generally provide a method and an apparatusimplementing adaptation of equalizer settings using error signalssampled at several different phases. In some embodiments, the apparatusmay include an inter symbol interference (ISI) cancellation circuit anda detector circuit. The inter symbol interference (ISI) cancellationcircuit is generally configured to minimize ISI at data sampling andcrossing sampling points in a symbol interval of an input signal. Aplurality of detector circuits may be configured to generate errorsamples at a plurality of phases. An adaptation circuit may beconfigured to adjust equalizer settings and/or sampling phases basedupon a data sample and the error samples. Embodiments of the inventionmay include providing a method and/or apparatus for implementingadaptation of equalizer settings using error signals sampled at severaldifferent phases that may (i) combine the best of center equalizationand edge equalization, (ii) be configurable to provide only centerequalization, only edge equalization or some combination of centerequalization and edge equalization, (iii) be used with both opticalchannel and backplane applications, (iv) have low implementation cost,and/or (v) be implemented with no additional analog circuits in systemshaving both bang-bang clock data recovery (CDR) and decision feedbackequalization (DFE).

Equalizer adaptation allows an equalizer to work at an optimal settingfor whatever channel the equalizer is connected to, without any humanintervention. There are two types of adaptation schemes. The differenceis mainly from the optimization goal. When an adaptation scheme aims tominimize the error at the data sampling point, the adaptation scheme iscalled center equalization. When an adaptation scheme aims to minimizejitter at the crossing sampling point (e.g., at a different samplingphase from the data sampling point, typically 90 degrees before or afterthe data sampling point, but some other phase difference is possible),the adaptation scheme is called edge equalization. Center equalizationtypically results in maximum vertical margin at the data sampling point,although this may not always be the case. Edge equalization typicallyresults in maximum horizontal margin, although this may not always bethe case.

Center equalization defines an error signal (e.g., EKD) as thedifference between a signal (e.g., RK) at an input of a detector and atarget level of a data sample (e.g., H0*DK) at the data sampling point(e.g., EKD=RK−H0*DK). In one example, an error capture latch may be usedto capture and sample the input signal RK at the data sampling phase.Edge equalization defines an error signal (e.g., EKX) based upon asignal sample (e.g., XK) sampled at a crossing sampling phase. The errorsignal may be determined, in one example, based upon whether atransition occurs between data samples (e.g., DK, DK(1)) sampled beforeand after the crossing sample XK. For example, the error signal may begenerated such that EKX=0 if DK=DK(1), that is no transition, and EKX=XKif there is a transition, DK=−DK(1). The crossing sample XK is the errorsampled at a particular phase. In one example, capture latches may beused to capture error samples at several different phases from the datasampling phase. The sampled signal(s) may be the same as the inputsignal to the data capture latch (e.g., R(t), RK, etc.), the signalbefore a DFE summing node (e.g., Y(t), YK, etc.), or one or more signalsfrom other points in the receiver path. In general, signals in the timedomain may be represented as functions of time (e.g., Y(T), R(T), F(T),etc.) and signals in the digital domain may be represented as samples(e.g., YK, RK, FK, EK, etc.).

Conventional adaptation techniques use either only center equalizationor only edge equalization. As a result, a compromise has to be madebetween the vertical and horizontal eye margins. Embodiments inaccordance with the invention combine the best of the two approaches byusing error signals sampled at both the data sampling phase and otherphases that are different from the data sampling phase. Embodiments ofthe invention may combine the two approaches in different ways. In oneexample, a linear combination of the mean squared error (MSE) of theerror signals sampled at different phases may be generated and the totalmean squared error minimized. For example, a function of the meansquared error of two error signals may be defined (e.g.,f(E[EK1^2],E[EK2^2])) and the output of the function minimized.

An embodiment of the invention may utilize adaptation of a continuoustime linear equalizer (CT-LE) gain to minimize a linear combination ofthe mean squared error of the error signals EK1 and EK2 sampled at twodifferent phases (e.g., ALPHA*E[EK1^2]+BETA*E[EK2^2]). Different ratiosof ALPHA and BETA may be used to provide different levels of tradeoffbetween the vertical and horizontal eye margins. In one example, anadaptation circuit may be implemented with values of ALPHA and BETA thatare configurable (e.g., automatically set or configured by users). Theimplementation of an adaptation circuit with configurable values forALPHA and BETA generally allows the same adaptation circuit to also beused in either center equalization only or edge equalization onlyapplications. For example, optical module interfaces prefer an edgeequalized linear equalizer and backplanes prefer a center equalizedlinear equalizer. To cover both applications, a conventional systemwould need to use two sets of adaptation circuits, with one of theadaptation circuits being disabled at any given time. In contrast toconventional approaches, an adaptation circuit implemented in accordancewith an embodiment of the invention could simply set BETA to 0 to getcenter equalization for backplanes and set ALPHA to 0 to get a edgeequalized linear equalizer for the optical channels. In an example withtwo error signals (e.g., EK1 and EK2), the corresponding gradient may beimplemented as (ALPHA*(−EK1)+BETA*EK2)*DK(I), where DK(I) refers to theIth data bit before the Kth bit, or the (K−I)th bit.

In some embodiments, four samples (e.g., I=2, 3, and 4) may be addedtogether and the sum used to adjust the gain of the linear equalizer.For example, the gradient may be implemented as(ALPHA*(−EK1)+BETA*EK2)*(DK(1)+DK(2)+DK(3)+DK(4)). The gradient may bepresented to the adaptation loop filter, which averages out thetransient changes and outputs the adjustment to the linear equalizergain.

Another embodiment is the adaptation of the DFE tap weights. In oneexample, a tap position h1 is still adapted using a gradient of−EK1*DK(1), while h2 and beyond are adapted using the gradient(ALPHA*(−EK1)+BETA*EK2)*DK(I)) with I being no less than 2. Since h2 andbeyond are adapted using the linear combination of mean squared error ofthe error signals sampled at two different phases, the converged tapweights have higher values than would be achieved from centerequalization, allowing the tap weights to reduce the mean squared error(e.g., at the crossing, which is E[EKX^2]= . . .+(P0.5−P−0.5−g1*H1)*DK(1)+(P1.5−H2)*DK(2)+(P2.5−H3)*DK(3)+ . . . . Ingeneral, making H2, H3, etc. larger reduces the terms (P1.5−H2),(P2.5−H3), . . . and consequently the mean squared error E[EKX^2].

Simulations confirm that the overall MSE is reduced with the new scheme.For simpler implementation in the digital domain, ALPHA and BETA may bechosen to be integers. For example, (ALPHA,BETA) may be (2,1), (4,1),(1,1) or (1,0), (0,1). In another embodiment of the invention, pole andgain of the CT-DFE may be adapted using doubled sampled error signals.

Although the settling point of bang-bang CDR is affected only by thefirst tap crossing ISI, the eye of the signal at the input to the datacapture latch is generally impacted by all the crossing ISI taps, whichmake the zero crossings spread over a wider region, reducing thehorizontal eye margin. Double rate DFE can cancel ISI at both datasampling point and at the zero crossings of the same input signal. It isyet another example how error signals sampled at different phases may beused. To adapt linear equalizers, a double rate virtual DFE may be used,which like the real double rate DFE, uses error signals sampled atdifferent phases. However, the double rate virtual DFE does not requirethe DFE circuit to run at twice the full data rate, nor does the doublerate virtual DFE require twice the feedback paths. In general, the errorsignals may be sampled at one or more phases. The greater the amount ofinformation that is available, the better the performance. One exampleis to sample before and after the zero crossing to obtain early and lateinformation.

Referring to FIG. 1, a block diagram of a system 100 is shownillustrating a communication system in which adaptation schemes inaccordance with embodiments of the invention may be implemented. Thesystem 100 may be implemented as multiple circuits or devices, or on anintegrated circuit. The system 100 may include a block (or circuit) 102,a block (or circuit) 104 and a block (or circuit) 106. The system 100may implement a serializer-deserializer (e.g., SerDes) apparatus. In aSerDes apparatus (or system), parallel data may be serialized in atransmitter (e.g., block 102), transferred as serial data on acommunication channel (e.g., block 104) and subsequently deserialized ina receiver (e.g., block 106) back into the parallel data. The blocks102-106 may represent modules and/or blocks that may be implemented ashardware, software, a combination of hardware and software, or otherimplementations. A signal (e.g., AK) may be received by the circuit 102.The signal AK may implement a data signal. A signal (e.g., DK) may begenerated by the circuit 106. The signal DK may carry recovered data.

The block 102 may implement a transmitter circuit. The block 102 isgenerally operational to generate signals carrying data to becommunicated to the block 106. The block 102 may also be operational toreceive signals carrying data received from the block 106. The signalsmay be communicated between the block 102 and the block 106 via theblock 104. The block 102 may be fabricated as one or more integratedcircuits. The block 104 may be fabricated as one or more of traces,wires, transmission lines, optical fiber, and wireless media. The block106 may be fabricated as one or more integrated circuits.

The circuit 102 may participate in a transmitter adaptation capabilityto account for channel pulse (or impulse) response characteristics ofthe circuit 104. A filter within the circuit 102 may be initiallyadapted to the circuit 104 based on an estimation of the channel pulseresponse. The adaptation generally involves adjusting one or more tapweights of the filter. After the initial adaptation, the adaptation maybe performed continuously to account for changing conditions in thecircuit 104. In some embodiments, the filter may be implemented as afinite impulse response (e.g., FIR) filter. Other filters may beimplemented to meet the criteria of a particular application.

The block 104 may implement a communication channel. The block 104 isgenerally operational to carry the data communicated from the block 102to the block 106. The block 104 may also carry data communicated fromthe block 106 to the block 102. The channel pulse responsecharacteristics of the block 104 generally cause distortions inamplitude and/or phase of the data signals as the data signals propagatefrom one port of the block 104 to the other. The channel pulse responsecharacteristics may also change over time and/or temperature.Implementations of the block 104 may include, but are not limited to,one or more transmission medium such as air, wire, transmission line,optical fibre, Ethernet and the like.

The block 106 may implement a receiver circuit. The block 106 isgenerally operational to receive signals from the block 102 via theblock 104. The block 106 may also be operational to send signals to theblock 102 via the block 104. The block 106 may include a receiveradaptation capability to account for the pulse response characteristicsof the blocks 102 and 104. One or more equalizers within the block 106may be initially adapted to the block 104 based on a sequence of pulses(or impulses) received from the block 102. The adaptation generallyinvolves adjusting one or more tap weights and/or programmable gainvalues of the equalizers. Once the tap weights have converged, the tapweights may be used as an estimate of the channel pulse responsecharacteristics of the block 104. The receiver adaptation may beperformed continuously to account for changing conditions in the block104. In some embodiments, the equalizers may be implemented as a linerequalizer (e.g., LE), continuous time liner equalizer (CT-LE), adecision feedback equalizer (e.g., DFE), and/or a continuous timedecision feedback equalizer (e.g., CT-DFE). Other types and numbers ofequalizers may be implemented to meet the criteria of a particularapplication.

Referring to FIG. 2, a diagram is shown illustrating a phaserelationship between a number of clock signals (e.g., CLK0, . . . ,CLKQ) and a data sampling input eye of an input signal (e.g., R(T)). Theclock signals CLK0, . . . , CLKQ may be implemented as individualsampling clocks, phases of a sampling clock signal, and/or anycombination thereof. In one example, rising edges of the clock signalsCLK1, . . . CLKQ generally occur some predetermined number of degreesrelative to (e.g., before or after) a rising edge of the clock signalCLK0. Clock signals with other phases may be implemented accordingly tomeet the design criteria of a particular implementation. The phase andfrequency of the clock signals CLK0, . . . , CLKQ may be adjusted suchthat the rising edge of the clock signal CLK0 corresponds with thecenter of a data input eye for the signal R(T) and the rising edges ofthe clock signals CLK1, . . . , CLKQ correspond with points between thecenter of a data input eye and the crossing point of the signal R(T).However, other relationships may be implemented accordingly to meet thedesign criteria of a particular implementation.

In various embodiments, a number of error samples (e.g., EK1, . . . EKQ,E(K+1)1, . . . , E(K+1)Q, etc.) comprise samples of the signal R(T)corresponding with respective rising edges of the signals (or phases)CLK1, . . . , CLKQ. Note that Q is used to represent the number of theerror samples and respective clock signals (e.g., CLK1, . . . , CLKQ,EK1, . . . , EKQ, E(K+1)1, . . . , E(K+1)Q, etc.) merely to avoidconfusion with other letters used to represent numbers of items (e.g.,L, M, N, etc.), and not meant to indicate any relationship between thenumber of the various items and the number of error samples that may beimplemented. The letters L, M, N, Q, etc. are used to indicate that anynumber of clocks, phases, taps, etc. may be implemented to meet thedesign criteria of a particular implementation.

Referring to FIG. 3, a diagram is shown illustrating relationshipsbetween phases of a sampling clock signal and the data sampling eye inthe 2T architecture. In one example, even data samples (e.g., DK, DK(2),etc.) may be generated by sampling a signal (e.g., E(T)) on the risingedge of the clock signal CLK0(2). Odd data samples (e.g., DK(1), DK(3),etc.) may be generated by sampling a signal (e.g., O(T)) on the risingedge of the clock signal CLK0. The corresponding error samples may begenerated similarly using the rising edges of a number of clock signals(or phases) CLK1, . . . , CLKQ and CLK(Q+1), . . . , CLK(2Q),respectively. In the 2T architecture (illustrated below in connectionwith FIGS. 12-14), the rising edges of the clock signals CLK1, . . . ,CLKQ occur some predetermined number of degrees relative to (e.g. beforeor after) the rising edge of the clock signal CLK0, the rising edges ofthe clock signals CLK(Q+1), . . . , CLK(2Q) occur some predeterminednumber of degrees relative to (e.g. before or after) the rising edge ofthe clock signal CLK0(2), and so on.

Referring to FIG. 4, a block diagram of a circuit 150 is shownillustrating an example receiver including a variety of features inaccordance with embodiments of the invention. The circuit 150 generallycomprises a block (or circuit) 152, a block (or circuit) 154, a block(or circuit) 156, a block (or circuit) 158, a block (or circuit) 160,and a block (or circuit) 162. The blocks 152-162 may represent modulesand/or blocks that may be implemented as hardware, software, acombination of hardware and software, or other implementations.

The block 152 may implement either a linear equalizer (LE) or acontinuous-time linear equalizer (CT-LE). The block 154 may beimplemented as an adder. The block 156 may be implemented as a datadetector (or latch). The block 158 may be implemented as either adiscrete decision feedback equalizer (DFE) or a continuous-time decisionfeedback equalizer (CT-DFE). The block 160 may be implemented as anerror sample generator. The block 162 may implement one or moreadaptation loops (e.g., LE, DFE, CDR, etc.) of the circuit 150.

The block 152 may receive a receiver input signal at a first input andpresent a first equalized signal (e.g., Y(T)) at an output. The block152 may have a second input through which a signal (e.g., LE ADJ) maycontrol a gain, pole and/or tap weight(s) of the block 152. The block154 may have a first input that may receive the signal Y(T), a secondinput that may receive a feedback signal (e.g., F(T)) and an output thatmay present a signal (e.g., R(T)). The block 154 may be configured togenerate the signal R(T) by subtracting the signal F(T) from the signalY(T) (e.g., R(T)=Y(T)−F(T)). The block 156 may have an input that mayreceive the signal R(T) and an output that may present a signal (e.g.,DK). The signal DK may carry data samples taken (e.g., recovered) fromthe signal R(T) during a data input eye. The block 158 may have an inputthat receives the signal DK and an output that presents the signal F(T).The block 158 may be configured to generate the signal F(T) in responseto the signal DK and a number of tap weights.

In some embodiments, the block 160 has an input that receives the signalR(T), a number of inputs that receive a number of clock signals (orphases) (e.g., CLK1, . . . , CLKQ) of a data sampling clock, and anumber of outputs that present a number of signals (e.g., EK1, . . . ,EKQ). The signals EK1, . . . , EKQ generally comprise error samples. Theblock 160 may be configured to generate the error samples EK1, . . . ,EKQ in response to the signal R(T), the phases CLK1, . . . , CLKQ, and apredetermined threshold.

In some embodiments, the block 162 has a first input that receives thesignal DK, a number of second inputs that receive the signals EK1, . . ., EKQ, a third input that receives a signal (e.g., ALPHA), and a fourthinput that receives a signal (e.g., BETA). The signal ALPHA may comprisea first coefficient. The signal BETA may comprise a second coefficient.The block 162 may be configured to implement adaptation loops thatdetermine (or adjust) one or more parameters (e.g., gain, pole, tapweight, etc.) of the blocks 152, 156, and 158 using the error samplesignals EK1, . . . , EKQ along with the first coefficient ALPHA and thesecond coefficient BETA. In one example, the block 162 may be configuredto implement a number of adaptation loops configured to determine anumber of tap weight values (e.g., H1-HN) for a number of DFE taps ofthe block 158. In another example, the block 162 may be configured toadjust a gain parameter, pole parameter, and/or tap weights of the block152. In still another example, the block 162 may be configured toimplement both a number of adaptation loops configured to determine anumber of tap weight values (e.g., H1-HN) for a number of DFE taps ofthe block 158 (or pole and gain parameters in the case of a CT-DFE) andan adaptation loop to adjust a gain parameter, pole parameter, and/ortap weights of the block 152.

Referring to FIG. 5, a block diagram of a circuit 150′ is shownillustrating another example receiver including a variety of features inaccordance with embodiments of the invention. The circuit 150′ may beimplemented similarly to the circuit 150, except that the block 160 isreplaced by a block 160′ that can receive (sample) the signal prior tothe summing node 154 (e.g., Y(T)) instead of or in addition to thesignal after the summing node 154 (e.g., R(T)). For example, the signalsY(T) and R(T) may be sampled using respective phases from the signalsCLK1, . . . , CLKQ. Other sampling points and/or multiple samplingpoints along the receiver path may be implemented accordingly to meetthe design criteria of a particular implementation.

Referring to FIG. 6, diagram of a module 170 is shown illustrating anerror signal generator in accordance with embodiments of the presentinvention. The module 170 may be implemented to generate a signal EK1and a signal EK2 based upon the signal Y(T) (or R(T)) and clock signals(or phases) CLK1 and CLK2. The module 170 may have a first input thatmay receive the signal Y(T) or R(T), a second input that may receive afirst clock signal CLK1, a third input that may receive a second clocksignal CLK2, a first output that may present the signal EK1, and asecond output that may present the signal EK2. In some embodiments, themodule 170 may comprise a block (or circuit) 172 and a block (orcircuit) 174. The block 172 may be implemented as a capture latch. Theblock 174 may be implemented as a capture latch. The blocks 172 and 174may have latch thresholds of 0.

The signal Y(T) or R(T) may be presented to a first input of the block172 and a first input of the block 174. A second input of the block 172may receive the clock signal or phase CLK1. A second input of the block174 may receive the signal or phase CLK2. The signals EK1 and EK2 may bepresented at respective outputs of the blocks 172 and 174.

Referring to FIG. 7, a block diagram of the circuit 180 is shownillustrating another example implementation of the error signalgenerator circuit in accordance with an example embodiment of theinvention. In one example, the error signal generator circuit 180 maycomprise a block (or circuit) 182, a block (or circuit) 184, a block (orcircuit) 186, and a block (or circuit) 188. The blocks 182, 184, and 186may be implemented as capture latches. The block 182 may be implementedhaving a crossing threshold of 0. The block 184 may be implementedhaving a crossing threshold of −H0. The block 186 may be implementedhaving a crossing threshold of H0. H0 generally represents a targetlevel for the receiver circuit 150. The block 188 may be implemented asa multiplexer.

An input signal R1(T) or Y1(T) may be presented to a first input of thecircuit 182. A clock signal CLK1 may be presented to a second input ofthe circuit 182. An output of the circuit 182 may present a first errorsample (e.g., EK1). An input signal Y2(t) or R2(T) may be presented to afirst input of the circuit 184 and a first input of the circuit 186. Anoutput of the circuit 184 may be presented to a first data input of thecircuit 188. An output of the circuit 186 may be presented to a secondinput of the circuit 188. A control input of the circuit 188 may receivethe signal DK. The circuit 188 may have an output that may present thesignal EK2. The signals Y1(T) and Y2(T) may be the same or differentsignals. The signals R1(T) and R2(T) may be the same or differentsignals.

Referring to FIG. 8, a block diagram of the circuit 190 is shownillustrating another example implementation of the error signalgenerator circuit in accordance with an example embodiment of theinvention. In some embodiments, the circuit 190 may have a number ofinputs that receive a plurality of clock signals or phases (e.g., CLK1,. . . , CLKQ), a number of inputs that receive one or more input signals(e.g., Y1(T), Y2(T), . . . , YQ(T) or R1(T), R2(T), . . . , RQ(T)), aninput that receives a data sample (e.g., DK), and a number of outputsthat present a plurality of error sample signals (e.g., EK1, . . . ,EKQ).

In one example, the error signal generator circuit 190 may comprise ablock (or circuit) 192, a number of blocks (or circuits) 194 a-194 m, anumber of blocks (or circuits) 196 a-196 m, and a number of blocks (orcircuits) 198 a-198 m. The blocks 192, 194 a-194 m, and 196 a-196 m maybe implemented as capture latches. The block 192 may be implementedhaving a crossing threshold of 0. The blocks 194 a-194 m may beimplemented having a crossing threshold of −H0. The block 196 a-196 mmay be implemented having a crossing threshold of H0. H0 generallyrepresents a target level for the receiver circuit 150. The blocks 198a-198 m may be implemented as multiplexers.

An input signal R1(T) or Y1(T) may be presented to a first input of thecircuit 192. A clock signal CLK1 may be presented to a second input ofthe circuit 192. An output of the circuit 192 may present a first errorsample (e.g., EK1). An input signal Y2(t) or R2(T) may be presented to afirst input of the circuit 194 a and a first input of the circuit 196 a.An output of the circuit 194 a may be presented to a first data input ofthe circuit 198 a. An output of the circuit 196 a may be presented to asecond input of the circuit 198 a. A control input of the circuit 198 amay receive the signal DK. The circuit 198 a may have an output that maypresent the signal EK2. The remaining circuits 194 b-194 m, 196 b-196 m,and 198 b-198 m may be configured similarly to generate the error samplesignals EK3, . . . , EKQ based on (i) the clock signals CLK3, . . . ,CLKQ, (ii) the inputs signals Y3(T), . . . , YQ(T) or R3(T), R2(T), . .. , RQ(T)), and the data sample DK. Any number, combination,permutation, etc. of the signals Y1(T), . . . , YQ(T) may be the same ordifferent signals. Any number, combination, permutation, etc. of thesignals R1(T), . . . , RQ(T) may be the same or different signals. Otherthresholds in addition to H0 and −H0 may be implemented to meet thedesign criteria of a particular implementation.

Referring to FIG. 9, a block diagram of the circuit 210 is shownillustrating an example implementation of an adaptation circuit inaccordance with an example embodiment of the invention. In someembodiments, the circuit 210 may be implemented as part of theadaptation block 162 of FIGS. 4 and 5. In some embodiments, the circuit210 comprises a block (or circuit) 211, a block (or circuit) 212, ablock (or circuit) 212, a block (or circuit) 214, a block (or circuit)215, and a block (or circuit) 216. The blocks 211, 212 and 215 may beimplemented as multipliers. In some embodiments, the block 213 may beimplemented as a latch. In other embodiments, the block 213 may beimplemented as an adder circuit. The block 214 may be implemented as anadder. The block 216 may implement a loop filter circuit. In oneexample, the block 216 may be configured to adjust one or moreparameters (e.g., gain, pole, tap weight(s), etc.) of a linear equalizer(LE) of a receiver.

The block 211 may be configured to generate a product of a first errorsample (e.g., EK1) and a first coefficient (e.g., ALPHA). The block 212may be configured to generate a product of a second error sample (e.g.,EK2) and a second coefficient (e.g., BETA). The block 214 may beconfigured to determined a difference between the product of the errorsample EK1 and the coefficient ALPHA and the product of the error sampleEK2 and the coefficient BETA (e.g., BETA*EK2−ALPHA*EK1). The block 213may be configured to store one or a sum of multiple data samples (e.g.,DK, SUM(DK(i), i=1, . . . , 4), etc.). In some embodiments, the block215 may implement a gradient (−ALPHA*EK1+BETA*EK2)*DK(I). In otherembodiments, the block 215 may implement a gradient(−ALPHA*EK1+BETA*EK2)*(DK(1)+DK(2)+DK(3)+DK(4)). The block 216 may beconfigured to adjust the parameters of the linear equalizer based uponthe gradient generated by the block 215.

Referring to FIG. 10, a block diagram of the circuit 220 is shownillustrating another example implementation of an adaptation circuit inaccordance with an example embodiment of the invention. In someembodiments, the circuit 220 may be implemented as part of theadaptation block 162 of FIGS. 4 and 5. In some embodiments, the circuit220 comprises a block (or circuit) 221, a block (or circuit) 222, ablock (or circuit) 223, a block (or circuit) 224, a block (or circuit)225, and a block (or circuit) 226. The blocks 221, 221 and 225 may beimplemented as multipliers. In some embodiments, the block 223 may beimplemented as a latch. In other embodiments, the block 223 may beimplemented as an adder circuit. The block 214 may be implemented as anadder. The block 226 may implement a loop filter circuit. In oneexample, the block 226 may be configured to adjust one or moreparameters (e.g., gain, pole, tap positions, tap weights, etc.) of adecision feedback equalizer (DFE) of a receiver.

The block 221 may be configured to generated a product of a first errorsample (e.g., EK1) and a first coefficient (e.g., ALPHA). The block 222may be configured to generated a product of a second error sample (e.g.,EK2) and a second coefficient (e.g., BETA). The block 224 may beconfigured to determined a difference between the product of the errorsample EK1 and the coefficient ALPHA and the product of the error sampleEK2 and the coefficient BETA (e.g., BETA*EK2−ALPHA*EK1). The block 223may be configured to store one or a sum of multiple data samples (e.g.,DK, SUM(DK(i), i=1, . . . , 4), etc.). In some embodiments, the block225 may implement a gradient (−ALPHA*EK1+BETA*EK2)*DK(I). In otherembodiments, the block 225 may implement a gradient(−ALPHA*EK1+BETA*EK2)*(DK(1)+DK(2)+DK(3)+DK(4)). The block 226 may beconfigured to adjust the parameters of the decision feedback equalizerbased upon the gradient generated by the block 225.

Referring to FIG. 11, a block diagram of the circuit 230 is shownillustrating still another example implementation of an adaptationcircuit in accordance with an example embodiment of the invention. Insome embodiments, the circuit 230 may be implemented as part of theadaptation block 162 of FIGS. 4 and 5. In some embodiments, the circuit230 comprises a number of blocks (or circuits) 232 a-232 n, a number ofblocks (or circuits) 234 a-234 n, a block (or circuit) 236, and a block(or circuit) 238. The blocks 232 a-232 n and 234 a-234 n may beimplemented as multipliers. The block 236 may implement an adder. Theblock 238 may implement a loop filter. In one example, the block 238 maybe configured to adjust one or more parameters (e.g., gain, pole, tapweight, etc.) of a linear equalizer (LE) of a receiver.

Each of the blocks 232 a-232 n may be configured to generated a productof a first error sample (e.g., EK1) and a respective data sample (e.g.,DK(1), . . . , DK(N1)). Each of the blocks 234 a-234 n may be configuredto generated a product of a second error sample (e.g., EK2) and arespective data sample (e.g., DK(1), . . . , DK(N2)). The block 236 maybe configured to generated a sum of the products generated by the blocks232 a-232 n and 234 a-234 n (e.g., EK1*DK(1) EK1*DK(2)+ . . .+EK1*DK(N1)+EK2*DK(1)+EK2*DK(2)+ . . . +EK2*DK(N2). The sum generated bythe block 236 may be employed by the block 238 to adjust one or moreparameters (e.g., gain, pole, tap weight, etc.) of a linear equalizer(LE) of a receiver.

Referring to FIG. 12, a block diagram of the circuit 240 is shownillustrating an example implementation of a clock and data recovery(CDR) circuit in accordance with an example embodiment of the invention.The circuit 240 may be implemented to adjust one or more sampling phasesof a receiver circuit. In some embodiments, the block 240 may beconfigured to utilize the error samples generated by the block 170(described above in connection with FIG. 6). For example, the block 240may be configured to adjust one or more sampling phases based on agradient determined by a first coefficient ALPHA, a second coefficientBETA and the plurality of error samples generated by the block 170.

Referring to FIG. 13, a block diagram of a circuit 300 is shownillustrating an example implementation of a half rate (2T) DFE andadaptation circuit in accordance with an example embodiment of theinvention. In one example, the circuit 300 may be implemented in aserializer/deserializer (SerDes) circuit. The circuit 300 may beimplemented as part of a receiver. The circuit 300 generally implementsa 2T-DFE structure comprising a first half and a second half. In oneexample, the first half of the circuit 300 may comprise a block (orcircuit) 302, a block (or circuit) 304, a block (or circuit) 306, ablock (or circuit) 310, a number of blocks (or circuits) 312 a-112 m,and a number of blocks (or circuits) 314 a-314 n. The second half of thecircuit 300 may comprise a block (or circuit) 303, a block (or circuit)305, a block (or circuit) 307, a number of blocks (or circuits) 313a-313 m, and a number of blocks (or circuits) 315 a-315 n. Each half ofthe circuit 300 implements a respective set of the total number of DFEtaps (e.g., N) used to provide decision feedback equalization. Each halfof the circuit 300 generates half of the total number of data samplesused for DFE. Each half of the circuit 300 generates half of the totalnumber of data and error samples used for adaptation of one or moreequalizers of the receiver in which the circuit 300 is implemented.Because each half of the circuit 300 generates only half of the datasamples, the two halves may operate at a lower speed (e.g., one-half thedata rate) than the data rate of the input signal (e.g., Y(T)). As wouldbe apparent to those skilled in the relavent art based upon thedescription herein, the architecture of the circuit 300 may be scaled toany nT architecture, where n is an integer (e.g., 1, 2, 3, 4, . . . ).The blocks 302 to 315 n may represent modules and/or blocks that may beimplemented as hardware, software, a combination of hardware andsoftware, or other implementations.

The blocks 302 and 303 may be implemented as adders. The blocks 304 and305 may be implemented as latches. The blocks 306 and 307 may beimplemented as error signal generators configured to generate aplurality of error signals (e.g., EK1, . . . , EKQ and E(K+1)1, . . . ,E(K+1)Q, respectively). The error signals EK1, . . . , EKQ and E(K+1)1,. . . , E(K+1)Q may be used by adaptation loops in the circuit 310 todetermine a number of tap weight values (e.g., H1-HN) for the respectiveDFE taps. The blocks 312 a-312 m and 313 a-313 m may implement sampleand hold or shift register elements. The blocks 314 a-314 n and 315a-315 n may be implemented as multipliers.

The block 302 may receive an input signal (e.g., Y(T)) at a first inputand a feedback signal (e.g., F1) at a second input. An output of theblock 302 may present a signal (e.g., O(T)) responsive to the inputsignal Y(T) and the feedback signal F1. The signal O(T) may be presentedas an input to the blocks 304 and 306. Specifically, the signal O(T) maybe sampled in response to a clock signal (e.g., CLK0) and the samplespresented to an input of the block 304. The signal O(T) may be sampledby the block 306 in response to a plurality of clock signals or phases(e.g., CLK1, . . . , CLKQ). The samples generated by the block 306 maybe presented to a first input of the block 310 as the signals EK1, . . ., EKQ. Note that Q is used to represent the number of the error samplesand respective clock signals (e.g., CLK1, . . . , CLKQ, EK1, . . . ,EKQ, E(K+1)1, . . . , E(K+1)Q, etc.) merely to avoid confusion withother letters used to represent numbers of items (e.g., L, M, N, etc.),and not meant to indicate any relationship between the number of thevarious items and the number of error samples that may be implemented.The letters L, M, N, Q, etc. are used to indicate that any number ofclocks, phases, taps, etc. may be implemented to meet the designcriteria of a particular implementation.

The block 304 may have a crossing threshold of zero. The block 304generally presents a positive (e.g., 1) output when the sampled signalis above the respective threshold and a negative (e.g., −1) output whenthe sampled signal is below the respective threshold. The output of theblock 304 may be randomly 1 or −1 when the respective input signal isvery close to the threshold value since the difference may be very smalland below the sensitivity of the latch (e.g., may take a very long timeto integrate to produce a signal that is large enough).

An output of the block 304 (e.g., DK) may be presented to a second inputof the block 310 and an input of the block 312 a. An output of the block312 a (e.g., DK(2)) may be presented to an input of the block 312 b, afirst input of the block 314 b, and a first input of the block 315 a. Anoutput of the block 312 b (e.g., DK(4)) may be presented to an input ofthe block 312 c (not shown), a first input of the block 314 d, and afirst input of the block 315 c. The blocks 312 c-312 m may be connectedsimilarly and may present respective data samples (e.g., DK(6), DK(8), .. . , DK(2L−2), DK(2L)). The block 314 a may have a second input thatmay receive a signal (e.g., H1). The signal H1 may represent a tapweight. The blocks 314 b-314 n may similarly receive respective tapweight signals (e.g., H2, H3, . . . , H(N−1), HN) and respective datasamples (e.g., DK(2), DK(3), . . . , DK(N−1), DK(N)).

The tap weights H1, H2, . . . , H(N−1), and HN may be determined throughadaptation based on the signals EK1, . . . , EKQ, E(K+1)1, . . . ,E(K+1)Q, DK, DK(1), DK(2), DK(3), . . . , DK(N−1), DK(N). In oneexample, the block 310 may implement an adaptation technique to adjustthe tap weights based on the error signals and the data samples. Theblocks 312 a-312 m and 314 a-314 n are generally part of a decisionfeedback equalizer that may be implemented using conventionaltechniques. Outputs of the blocks 314 a-314 n generally presentcomponents of the feedback signal F1 presented to the second input ofthe block 302.

The block 303 may receive the input signal Y(T) at a first input and afeedback signal (e.g., F2) at a second input. An output of the block 303may present a signal (e.g., E(T)) responsive to the input signal Y(T)and the feedback signal F2. The signal E(T) may be presented as an inputto the blocks 305 and 307. Specifically, the signal E(T) may be sampledin response to a clock signal (e.g., CLK0(2)) and the samples presentedto an input of the block 305. The signal E(T) may be sampled by theblock 307 in response to a plurality of clock signals or phases (e.g.,CLK(Q+1), . . . , CLK(2Q)). The samples generated by the block 307 arepresented to a third input of the block 310 as signals E(K+1)1, . . . ,E(K+1)Q.

The block 305 may have a crossing threshold of zero. The block 305generally presents a positive (e.g., 1) output when the sampled signalis above the respective threshold and a negative (e.g., −1) output whenthe sampled signal is below the respective threshold. The output of theblock 305 may be randomly 1 or −1 when the respective input signal isvery close to the threshold value since the difference may be very smalland below the sensitivity of the latch (e.g., may take a very long timeto integrate to produce a signal that is large enough).

An output of the block 305 (e.g., DK(1)) may be presented to a fourthinput of the block 310, an input of the block 313 a, and a second inputof the block 314 a. An output of the block 313 a (e.g., DK(3)) may bepresented to an input of the block 313 b, a first input of the block 315b, and an input of the block 314 c. An output of the block 313 b (e.g.,DK(5)) may be presented to an input of the block 313 c (not shown), afirst input of the block 315 d, and an input of the block 314 d. Theblocks 313 c-313 m may be connected similarly and may present respectivedata samples (e.g., DK(7), DK(9), etc.). The last respective data samplepresented by the blocks 313 c-313 m generally depends upon whether N iseven or odd. When N is even, the last respective data sample isDK(2L+1), where L=N/2. When N is odd, the last respective data sample isDK(2L−1), because N/2 is not an integer and L is set to the next higherinteger (e.g., L=3 when N=5). The block 315 a may have a second inputthat may receive the signal H1. The signal H1 may represent a tapweight. The blocks 315 b-315 n may similarly receive respective tapweight signals (e.g., H2, H3, . . . , H(N−1), H(N)) and respective datasamples (e.g., DK(3), DK(4), DK(N), DK(N+1)).

The blocks 313 a-313 m and 315 a-315 n are generally part of a decisionfeedback equalizer that may be implemented using conventionaltechniques. Outputs of the blocks 315 a-315 n generally presentcomponents of the feedback signal F2 presented to the second input ofthe block 303. The block 310 may have an output that may present asignal that may adjust parameters of one or more equalizers of thereceiver circuit.

Referring to FIG. 14, a block diagram of a circuit 420 is shownillustrating an alternative example of a 2T architecture DFE andadaptation circuit in accordance with another example embodiment of theinvention. The circuit 420 may be implemented similarly to the circuit300, except that the error samples are taken prior to the DFE summingnodes. The circuit 420 generally implements a 2T-DFE structurecomprising a first half and a second half. In one example, the firsthalf of the circuit 420 may comprise a block (or circuit) 422, a block(or circuit) 424, a block (or circuit) 426, a block (or circuit) 430, anumber of blocks (or circuits) 432 a-432 m, and a number of blocks (orcircuits) 434 a-434 n. The second half of the circuit 420 may comprise ablock (or circuit) 423, a block (or circuit) 425, a block (or circuit)427, a number of blocks (or circuits) 433 a-433 m, and a number ofblocks (or circuits) 435 a-435 n. Each half of the circuit 420 generallyimplements a respective set of the total number of DFE taps (e.g., N)used to provide decision feedback equalization. Each half of the circuit420 may generate half of the total number of data samples used for DFE.Because each half of the circuit generates only half of the datasamples, the two halves may operate at a lower speed (e.g., one-half thedata rate) than the data rate of the input signal (e.g., Y(T)). As wouldbe apparent to those skilled in the relavent art based upon thedescription herein, the architecture of the circuit 420 may be scaled toany nT architecture, where n is an integer (e.g., 1, 2, 3, . . . ). Thecircuits 422 to 435 n may represent modules and/or blocks that may beimplemented as hardware, software, a combination of hardware andsoftware, or other implementations.

The circuits 422 and 423 may be implemented as adders. The circuits 424and 425 may be implemented as error signal generators. The circuits 426and 427 may be implemented as data latches. The circuits 424 and 425 mayimplement are configured to generate a plurality of error signals orsamples (e.g., EK1, . . . , EKQ and E(K+1)1, E(K+1)Q, respectively). Theerror signals EK1, . . . , EKQ and E(K+1)1, E(K+1)Q may be used byadaptation loops of the block 430 to determine a number of tap weightvalues (e.g., H1-HN) for the respective DFE taps. The circuits 432 a-432m and 433 a-433 m may implement sample and hold or shift registerelements. The circuits 434 a-434 n and 435 a-435 n may be implemented asmultipliers. Note that Q is used to represent the number of the errorsamples and respective clock signals (e.g., CLK1, . . . , CLKQ, EK1, . .. , EKQ, E(K+1)1, E(K+1)Q, etc.) merely to avoid confusion with otherletters used to represent numbers of items (e.g., L, M, N, etc.), andnot meant to indicate any relationship between the number of the variousitems and the number of error samples that may be implemented. Theletters L, M, N, Q, etc. are used to indicate that any number of clocks,phases, taps, etc. may be implemented to meet the design criteria of aparticular implementation.

The circuit 422 may receive the input signal (e.g., Y(T)) at a firstinput and a feedback signal (e.g., F1) at a second input. An output ofthe circuit 422 may present a signal (e.g., E(T)) responsive to theinput signal Y(T) and the feedback signal F1. The signal Y(T) is presentto an input of the circuit 424. The signal E(T) may be presented as aninput to the circuit 426. Specifically, the signal Y(T) may be sampledby the circuit 424 in response to a plurality of clock signals or phases(e.g., CLK1, . . . , CLKQ) and the samples presented to a first input ofthe circuit 430 as the signals EK1, . . . , EKQ. The signal E(T) may besampled in response to a clock signal (e.g., CLK0) and the samplespresented to an input of the circuit 426.

The circuit 426 may have a crossing threshold of zero. The circuit 426generally present a positive (e.g., 1) output when the sampled signal isabove the respective threshold and a negative (e.g., −1) output when thesampled signal is below the respective threshold. The output of thecircuit 426 is randomly 1 or −1 when the respective input signal is veryclose to the threshold value since the difference may be very small andbelow the sensitivity of the latch (e.g., may take a very long time tointegrate to produce a signal that is large enough).

An output of the circuit 426 (e.g., DK) may be presented to a secondinput of the circuit 430 and an input of the circuit 432 a. An output ofthe circuit 432 a (e.g., DK(2)) may be presented to an input of thecircuit 432 b, a first input of the circuit 434 b, and a first input ofthe circuit 435 a. An output of the circuit 432 b (e.g., DK(4)) may bepresented to an input of the circuit 432 c (not shown), a first input ofthe circuit 434 d, and a first input of the circuit 435 c. The circuits432 c-432 m may be connected similarly and may present respective datasamples (e.g., DK(6), DK(8), . . . , DK(2L−2), DK(2L)). The circuit 434a may have a second input that may receive a signal (e.g., H1). Thesignal H1 may represent a tap weight. The circuits 434 b-434 n maysimilarly receive respective tap weight signals (e.g., H2, H3, . . . ,H(N−1), HN) and respective data samples (e.g., DK(2), DK(3), . . . ,DK(N−1), DK(N)).

The tap weights H1, H2, . . . , H(N−1), and HN may be determined throughadaptation based on signals EK1, . . . , EKQ, E(K+1)1, . . . , E(K+1)Q,DK, DK(1), DK(2), DK(3), . . . , DK(N−1), DK(N). In one example, asign-sign LMS technique may be used to adjust the tap weights based onthe error samples and the data samples. The circuits 432 a-432 m and 434a-434 n are generally part of a decision feedback equalizer that may beimplemented using conventional techniques. Outputs of the circuits 434a-434 n generally present components of the feedback signal F1 presentedto the second input of the circuit 422.

The circuit 423 may receive the input signal Y(T) at a first input and afeedback signal (e.g., F2) at a second input. An output of the circuit423 may present a signal (e.g., O(T)) responsive to the input signalY(T) and the feedback signal F2. The signal Y(T) may be presented as aninput to the circuit 425. The signal O(T) may be presented as an inputto the circuits 427. Specifically, the signal Y(T) may be sampled by thecircuit 425 in response to a plurality of clock signals or phases (e.g.,CLK(Q+1), . . . , CLK(2Q). The samples generated by the circuit 425 maybe presented to a third input of the circuit 430 as the signals E(K+1)1,. . . , E(K+1)Q. The signal O(T) may be sampled in response to a clocksignal (e.g., CLK0(2)) and the samples presented to an input of thecircuit 427. In one example, the clock signals CLK0 and CLK0(2) may beimplemented as different phases of a single sampling clock signal.

The circuit 427 may have a crossing threshold of zero. The circuit 427generally presents a positive (e.g., 1) output when the sampled signalis above the respective threshold and a negative (e.g., −1) output whenthe sampled signal is below the respective threshold. The output of thecircuit 427 is randomly 1 or −1 when the respective input signal is veryclose to the threshold value since the difference may be very small andbelow the sensitivity of the latch (e.g., may take a very long time tointegrate to produce a signal that is large enough).

An output of the circuit 427 (e.g., DK(1)) may be presented to a fourthinput of the circuit 430, an input of the circuit 433 a, and a secondinput of the circuit 434 a. An output of the circuit 433 a (e.g., DK(3))may be presented to an input of the circuit 433 b, an input of thecircuit 434 c, and a first input of the circuit 435 b. An output of thecircuit 433 b (e.g., DK(5)) may be presented to an input of the circuit433 c (not shown), an input of the circuit 434 e (not shown), and afirst input of the circuit 435 d. The circuits 433 c-433 m may beconnected similarly and may present respective data samples (e.g.,DK(7), DK(9), etc.). The last respective data sample presented by thecircuits 433 c-433 m generally depends on whether N is even or odd. WhenN is even, the last respective data sample is DK(2L+1), where L=N/2.When N is odd, the last respective data sample is DK(2L−1), because N/2is not an integer and L is set to the next higher integer (e.g., L=3when N=5). The circuit 435 a may have a second input that may receivethe signal H1. The signal H1 may represent a tap weight. The circuits435 b-435 n may similarly receive respective tap weight signals (e.g.,H2, H3, . . . , H(N−1), H(N)) and respective data samples (e.g., DK(3),DK(4), . . . , DK(N), DK(N+1)). The circuits 433 a-433 m and 435 a-435 nare generally part of a decision feedback equalizer that may beimplemented using conventional techniques. Outputs of the circuits 435a-435 n generally present components of the feedback signal F2 presentedto the second input of the circuit 423.

The circuit 430 may have an output that may present a signal that may beused to adjust one or more parameters of one or more equalizers of areceiver. In one example, the circuit 430 may be configured to implementa gradient function described above. The circuit 430 generally uses thesignals received from the circuits 424-427. In general, the 2Tarchitecture presents four inputs to the circuit 430 during every twosymbol periods. For example, one data sample and a number of errorsamples are presented every symbol period, which are used by the circuit430 to adapt equalizer parameters as described above.

Referring to FIG. 15, a block diagram of a circuit 500 is shownillustrating another example implementation of bang-bang CDR and DFE inaccordance with another example embodiment of the invention. In oneexample, the circuit 500 may be implemented in a serializer/deserializer(SerDes) circuit. The circuit 500 may be implemented as part of areceiver. The circuit 500 generally implements a 2T-DFE structurecomprising a first half and a second half. In one example, the firsthalf of the circuit 500 may comprise a block (or circuit) 502, a block(or circuit) 504, a block (or circuit) 506, a block (or circuit) 508, ablock (or circuit) 510, a number of blocks (or circuits) 512 a-512 m,and a number of blocks (or circuits) 514 a-514 n. The second half of thecircuit 500 may comprise a block (or circuit) 503, a block (or circuit)505, a block (or circuit) 507, a block (or circuit) 509, a number ofblocks (or circuits) 513 a-513 m, and a number of blocks (or circuits)515 a-515 n. Each half of the circuit 500 generally implements arespective set of the total number of DFE taps (e.g., N) used to providedecision feedback equalization. Each half of the circuit 500 maygenerate half of the total number of data samples used for DFE. Becauseeach half of the circuit generates only half of the data samples, thetwo halves may operate at a lower speed (e.g., one-half the data rate)than the data rate of the input signal (e.g., Y(T)). As would beapparent to those skilled in the relavent art based upon the descriptionherein, the architecture of the circuit 500 may be scaled to any nTarchitecture, where n is an integer (e.g., 1, 2, 3, . . . ). Thecircuits 502 to 515 n may represent modules and/or blocks that may beimplemented as hardware, software, a combination of hardware andsoftware, or other implementations.

The circuits 502 and 503 may be implemented as adders. The circuits 504and 505 may be implemented as crossing latches. The circuits 506 and 507may be implemented as data latches. Each of the circuits 508 and 509 mayimplement an error signal generator configured to generate a pluralityof error signals or samples (e.g., EKA1, . . . , EKAQ and EKB1, . . . ,EKBQ, respectively). The error signals EKA1, . . . , EKAQ and EKB1, . .. , EKBQ may be used by adaptation loops configured to determine anumber of tap weight values (e.g., H1-HN) for the respective DFE taps.The circuit 510 may implement a bang-bang phase detector (PD) usingconventional techniques. The circuits 512 a-512 m and 513 a-513 m mayimplement sample and hold or shift register elements. The circuits 514a-514 n and 515 a-515 n may be implemented as multipliers.

The circuit 502 may receive an input signal (e.g., Y(T)) at a firstinput and a feedback signal (e.g., FK1) at a second input. An output ofthe circuit 502 may present a signal (e.g., E(T)) responsive to theinput signal Y(T) and the feedback signal FK1. The signal E(T) may bepresented as an input to the circuits 504, 506, and 508. Specifically,the signal E(T) may be sampled in response to a first clock signal(e.g., CLK3) and the samples presented to an input of the circuit 504.The signal E(T) may be sampled also in response to a second clock signal(e.g., CLK2) and the samples presented to an input of the circuit 506.The circuit 508 may be configured to sample the signal E(T) in responseto a number of clock signals or phases (e.g., CLKA1, . . . , CLKAQ). Thesamples generated by the circuit 508 may be presented as the errorsignals (or samples) EKA1, . . . , EKAQ.

The circuits 504 and 506 may have a crossing threshold of zero. Thecircuits 504 and 506 generally present a positive (e.g., 1) output whenthe sampled signal is above the respective threshold and a negative(e.g., −1) output when the sampled signal is below the respectivethreshold. The output of the latches 504 and 506 is randomly 1 or −1when the respective input signals are very close to the threshold valuesince the difference may be very small and below the sensitivity of thelatch (e.g., may take a very long time to integrate to produce a signalthat is large enough).

An output of the circuit 504 (e.g., XK(1) or XK(−1)) may be presented toa first input of the circuit 510. An output of the circuit 506 (e.g.,DK) may be presented to a second input of the circuit 510 and an inputof the circuit 512 a. An output of the circuit 512 a (e.g., DK(2)) maybe presented to an input of the circuit 512 b, a first input of thecircuit 514 b, and a first input of the circuit 515 a. An output of thecircuit 512 b (e.g., DK(4)) may be presented to an input of the circuit512 c (not shown), a first input of the circuit 514 d, and a first inputof the circuit 515 c. The circuits 512 c-512 m may be connectedsimilarly and may present respective data samples (e.g., DK(6), DK(8), .. . , DK(2L−2), DK(2L)). The circuit 514 a may have a second input thatmay receive a signal (e.g., H1). The signal H1 may represent a tapweight. The circuits 514 b-514 n may similarly receive respective tapweight signals (e.g., H2, H3, . . . , H(N−1), HN) and respective datasamples (e.g., DK(2), DK(3), DK(N−1), DK(N)).

The tap weights H1, H2, . . . , H(N−1), and HN may be determined throughadaptation based on the signals EKA1, EKAQ, EKB1, . . . , EKBQ, DK,DK(1), DK(2), DK(3), . . . , DK(N−1), DK(N). In one example, a sign-signLMS technique may be used to adjust the tap weights based on the errorsamples and the data samples. The circuits 512 a-512 m and 514 a-514 nare generally part of a decision feedback equalizer that may beimplemented using conventional techniques. Outputs of the circuits 514a-514 n generally present components of the feedback signal FK1presented to the second input of the circuit 502.

The circuit 503 may receive the input signal Y(T) at a first input and afeedback signal (e.g., FK2) at a second input. An output of the circuit503 may present a signal (e.g., O(T)) responsive to the input signalY(T) and the feedback signal FK2. The signal O(T) may be presented as aninput to the circuits 505, 507, and 509. Specifically, the signal O(T)may be sampled in response to a third clock signal (e.g., CLK1) and thesamples presented to an input of the circuit 505. The signal O(T) may besampled also in response to a fourth clock signal (e.g., CLK0) and thesamples presented to an input of the circuit 507. The circuit 509 maysample the signal O(T) in response to a plurality of clock signals orphases (e.g., CLKB1, . . . , CLKBQ). In one example, the clock signalsmay be implemented generally as different phases of a sampling clocksignal.

The circuits 505 and 507 may have a crossing threshold of zero. Thecircuits 505 and 507 generally present a positive (e.g., 1) output whenthe sampled signal is above the respective threshold and a negative(e.g., −1) output when the sampled signal is below the respectivethreshold. The output of the latches 505 and 507 is randomly 1 or −1when the respective input signals are very close to the threshold valuesince the difference may be very small and below the sensitivity of thelatch (e.g., may take a very long time to integrate to produce a signalthat is large enough).

An output of the circuit 505 (e.g., XK) may be presented to a thirdinput of the circuit 510. An output of the circuit 507 (e.g., DK(1)) maybe presented to a fourth input of the circuit 510, an input of thecircuit 513 a, and a second input of the circuit 514 a. An output of thecircuit 513 a (e.g., DK(3)) may be presented to an input of the circuit513 b, an input of the circuit 514 c, and a first input of the circuit515 b. An output of the circuit 513 b (e.g., DK(5)) may be presented toan input of the circuit 513 c (not shown), an input of the circuit 514 e(not shown), and a first input of the circuit 515 d. The circuits 513c-513 m may be connected similarly and may present respective datasamples (e.g., DK(7), DK(9), etc.). The last respective data samplepresented by the circuits 513 c-513 m generally depends on whether N iseven or odd. When N is even, the last respective data sample isDK(2L+1), where L=N/2. When N is odd, the last respective data sample isDK(2L−1), because N/2 is not an integer and L is set to the next higherinteger (e.g., L=3 when N=5). The circuit 515 a may have a second inputthat may receive the signal H1. The signal H1 may represent a tapweight. The circuits 515 b-515 n may similarly receive respective tapweight signals (e.g., H2, H3, . . . , H(N−1), H(N)) and respective datasamples (e.g., DK(3), DK(4), DK(N), DK(N+1)). The circuits 513 a-513 mand 515 a-515 n are generally part of a decision feedback equalizer thatmay be implemented using conventional techniques. Outputs of thecircuits 515 a-515 n generally present components of the feedback signalFK2 presented to the second input of the circuit 503.

The circuit 510 may have an output that may present a signal (e.g.,PHASE ADJUST) that may be used to adjust the phase of the samplingclock(s) and, consequently, the sampling phases of the circuit 500. Inone example, the circuit 510 may be configured to implement a transferfunction that may be summarized by the following TABLE 1:

TABLE 1 PHASE UP XK DK(1) DK OR DOWN 1 1 −1 1 −1 1 −1 −1 1 −1 1 −1 −1 −11 1 1 1 1 0 −1 1 1 −1 −1 −1 −1 0 1 −1 −1 −1The circuit 510 generally uses three of the four signals received fromthe latches 504-507. In general, the 2T architecture presents fourinputs to the circuit 510 during every two symbol periods. For example,one data sample and one crossing sample are present every symbol period,which are used by the circuit 510 as illustrated in TABLE 1 above. Thecircuit 510 generally implements a sliding window technique that adjuststhe sampling phase of the circuit 500 using three of the four signals.In another example, the circuit 510 may be replaced with the phaseadjustment circuit illustrated in FIG. 12.

Referring to FIG. 16, a flow diagram is shown illustrating a process (ormethod) 600 for adapting equalizer parameters of a receiver circuit inaccordance with an example embodiment of the invention. The process 600may comprise a step (or state) 602, a step (or state) 604, and a step(or state) 606. The step 602 may comprise determining a value for afirst coefficient ALPHA and a second coefficient BETA. The values of thecoefficients ALPHA and BETA may be predetermined (e.g., based onmeasurements of a DFE feedback waveform, etc.) or set based upon userinput. When the values of the coefficients ALPHA and BETA have beendetermined, the process 600 may move to the step 604. In the step 604,the process 600 generates a plurality of error signals (e.g., EK1, . . ., EKQ) for every symbol. When the error signals for a symbol have beengenerated, the process 600 may move to the step 606. In the step 606,the process 600 adjusts one or more equalizer parameters (e.g., gain,pole, tap weights, etc.) of the receiver circuit. In one example, theadjustments to the equalizer parameters may be based upon a gradient(ALPHA*(−EK1)+BETA*(EKQ))*DK(1). However, other gradients employing aplurality of error samples may be implemented accordingly to meet thedesign criteria of a particular implementation.

Embodiments of the invention generally provide a method and/or apparatusfor implementing adaptation of equalizer settings using error signalssampled at several different phases that may (i) combine the best of thecenter equalization and edge equalization, (ii) be configurable to haveonly center equalization, only edge equalization or a combination ofcenter equalization and edge equalization, and/or (iii) have lowimplementation cost. The ability to have only center equalization, onlyedge equalization or a combination of center equalization and edgeequalization is useful because different applications have differentneeds. For example, optical channels prefer edge equalized linearequalizers, while backplanes have better performance with center edgeequalized linear equalizers. The implementation cost may be low because,when both bang-bang CDR and DFE are employed, error signals that aresampled 90 degrees apart are already available. Since the error signalsare already available, no additional analog circuits are needed.

Referring to FIG. 17, a diagram is shown illustrating a DFE feedbackwaveform. When bang-bang CDR is used together with a DFE, couplingbetween the bang-bang CDR and the DFE may occur. The DFE feedback is notonly applied at the data sample, but also at error and crossing samplesprior to the data sample and following the data sample. In general, asignificant portion of the DFE feedback may be applied at the othersampling points. For example, if the first tap DFE feedback applied atthe data sample is expressed as H1*DK(1), the DFE feedback applied atthe prior sample point may be expressed as ALPHA*H1*DK(1), where ALPHAmay range from 40% to 90%, depending on the implementation. After thefeedback (e.g., H1*DK(1)) reaches its full level, the feedback isgenerally reduced to zero. However, the feedback does not reach zeroinstantaneously. The DFE feedback applied at the subsequent sample pointmay be expressed as BETA*H1*DK(1), where BETA may range from 0% to 100%,depending on the implementation. The terms ALPHA and BETA are used toindicate that different amounts of feedback may be applied at the risingand the falling edges.

In general, for a 2T architecture BETA in the analysis shows that usingthe right crossing sample has no coupling from the DFE. Although XK(−1)may include the BETA term, the BETA term is averaged out since DK(1) isuncorrelated with DK. Also, when the right crossing is used, DK=−DK(−1)and is uncorrelated with DK(1). When the left crossing is used,DK=−DK(1), so DK is correlated with DK(1). For a 1T architecture, XK(−1)will have both ALPHA and BETA terms. In an nT architecture where n>1,the ALPHA term drops out because the DFE feedback is in a differentbranch.

The functions illustrated by the diagrams of FIGS. 4-16 may beimplemented (e.g., performed, simulated, realized, etc.) using one ormore of a conventional general purpose processor, digital computer,microprocessor, microcontroller, RISC (reduced instruction set computer)processor, CISC (complex instruction set computer) processor, SIMD(single instruction multiple data) processor, signal processor, centralprocessing unit (CPU), arithmetic logic unit (ALU), video digital signalprocessor (VDSP) and/or similar computational machines, programmedaccording to the teachings of the present specification, as will beapparent to those skilled in the relevant art(s). Appropriate software,firmware, coding, routines, instructions, opcodes, microcode, and/orprogram modules may readily be prepared by skilled programmers based onthe teachings of the present disclosure, as will also be apparent tothose skilled in the relevant art(s). The software is generally executedfrom a medium or several media by one or more of the processors of themachine implementation.

Embodiments of the invention may also be implemented by the preparationof ASICs (application specific integrated circuits), Platform ASICs,FPGAs (field programmable gate arrays), PLDs (programmable logicdevices), CPLDs (complex programmable logic device), sea-of-gates, RFICs(radio frequency integrated circuits), ASSPs (application specificstandard products), one or more monolithic integrated circuits, one ormore chips or die arranged as flip-chip modules and/or multi-chipmodules or by interconnecting an appropriate network of conventionalcomponent circuits, as is described herein, modifications of which willbe readily apparent to those skilled in the art(s).

Embodiments of the invention thus may also include a computer productwhich may be a storage medium or media and/or a transmission medium ormedia including instructions which may be used to program a machine toperform one or more processes or methods in accordance with theinvention. Execution of instructions contained in the computer productby the machine, along with operations of surrounding circuitry, maytransform input data into one or more files on the storage medium and/orone or more output signals representative of a physical object orsubstance, such as an audio and/or visual depiction. The storage mediummay include, but is not limited to, any type of disk including floppydisk, hard drive, magnetic disk, optical disk, CD-ROM, DVD andmagneto-optical disks and circuits such as ROMs (read-only memories),RAMS (random access memories), EPROMs (erasable programmable ROMs),EEPROMs (electrically erasable programmable ROMs), UVPROM (ultra-violeterasable programmable ROMs), Flash memory, magnetic cards, opticalcards, and/or any type of media suitable for storing electronicinstructions.

The elements of various embodiments of the invention may form part orall of one or more devices, units, components, systems, machines and/orapparatuses. The devices may include, but are not limited to, servers,workstations, storage array controllers, storage systems, personalcomputers, laptop computers, notebook computers, palm computers,personal digital assistants, portable electronic devices, batterypowered devices, set-top boxes, encoders, decoders, transcoders,compressors, decompressors, pre-processors, post-processors,transmitters, receivers, transceivers, cipher circuits, cellulartelephones, digital cameras, positioning and/or navigation systems,medical equipment, heads-up displays, wireless devices, audio recording,audio storage and/or audio playback devices, video recording, videostorage and/or video playback devices, game platforms, peripheralsand/or multi-chip modules. Those skilled in the relevant art(s) wouldunderstand that the elements of the invention may be implemented inother types of devices to meet the criteria of a particular application.

The terms “may” and “generally” when used herein in conjunction with“is(are)” and verbs are meant to communicate the intention that thedescription is exemplary and believed to be broad enough to encompassboth the specific examples presented in the disclosure as well asalternative examples that could be derived based on the disclosure. Theterms “may” and “generally” as used herein should not be construed tonecessarily imply the desirability or possibility of omitting acorresponding element.

While embodiments of the invention have been particularly shown anddescribed with reference to the figures, it will be understood by thoseskilled in the art that various changes in form and details may be madewithout departing from the scope of the invention.

The invention claimed is:
 1. An apparatus comprising: an error samplegenerating circuit comprising a plurality of detector circuits, each ofsaid plurality of detector circuits configured to generate a respectiveerror sample in response to a respective one of a plurality of phases;and an adaptation circuit configured to adjust one or more equalizersettings based upon a data sample and the error samples, wherein saidadaptation circuit is further configured to generate a phase adjustmentsignal.
 2. The apparatus according to claim 1, further comprising adecision feedback equalizer (DFE).
 3. The apparatus according to claim1, further comprising a linear equalizer (LE).
 4. The apparatusaccording to claim 3, wherein said one or more equalizer settingscomprise at least one of a gain, a pole and a tap weight.
 5. Theapparatus according to claim 1, wherein said one or more equalizersettings comprise tap weights of a decision feedback equalizer (DFE). 6.The apparatus according to claim 1, wherein said one or more equalizersettings comprise pole and gain of a continuous-time decision feedbackequalizer (CT-DFE).
 7. The apparatus according to claim 1, wherein saiderror sample generating circuit generates said error samples based uponeither an output of a linear equalizer, an output of a summing nodeconfigured to combine said output of said linear equalizer with anoutput of a decision feedback equalizer, or said output of said linearequalizer and said output of said summing node.
 8. The apparatusaccording to claim 1, wherein said adaptation circuit is furtherconfigured to: generate a first product by multiplying a first errorsample by a first coefficient; generate a second product by multiplyinga second error sample by a second coefficient; generate a third productby multiplying a difference of said first product and said secondproduct by said data sample; and adjust a gain of a linear equalizerbased upon said third product.
 9. The apparatus according to claim 1,wherein said adaptation circuit is further configured to generate afirst product by multiplying a first error sample by a firstcoefficient; generate a second product by multiplying a second errorsample by a second coefficient; generate a third product by multiplyinga difference of said first product and said second product by said datasample; and adjust one or more tap weights of a decision feedbackequalizer or pole and gain of a continuous-time decision feedbackequalizer (CT-DFE) based upon said third product.
 10. The apparatusaccording to claim 1, wherein said adaptation circuit is furtherconfigured to; generate a first product by multiplying a first errorsample by a first coefficient; generate a second product by multiplyinga second error sample by a second coefficient; generate a third productby multiplying a difference of said first product and said secondproduct with a plurality of previous data samples; and adjust one ormore of a gain, a pole, and a tap weight of a linear equalizer basedupon said third product.
 11. The apparatus according to claim 1, whereinsaid adaptation circuit is further configured to: generate a firstproduct by multiplying a first error sample by a first coefficient;generate a second product by multiplying a second error sample by asecond coefficient; generate a third product by multiplying a differenceof said first product and said second product with a plurality ofprevious data samples; and adjust one or more tap weights of a decisionfeedback equalizer or pole and gain of a continuous-time decisionfeedback equalizer (CT-DFE) based upon said third product.
 12. Theapparatus according to claim 1, wherein said adaptation circuit isfurther configured to: generate a plurality of first products bymultiplying a first error sample by a plurality of first data samples;generate a plurality of second products by multiplying a second errorsample by a plurality of second data samples; and adjust one or more ofa gain, a pole, and a tap weight of an equalizer based upon a sum ofsaid plurality of first products and said plurality of second products.13. A method of adjusting equalizer settings in a receiver pathcomprising the steps of: generating a plurality of error samples at aplurality of phases; adjusting one or more of said equalizer settings ofsaid receiver path based upon a data sample and said plurality of errorsamples; generating a first product by multiplying a first error sampleby a first coefficient; generating a second product by multiplying asecond error sample by a second coefficient; generating a third productby multiplying a difference of said first product and said secondproduct by said data sample; and adjusting one or more of a gain, apole, and a tap weight of a linear equalizer based upon said thirdproduct.
 14. The method according to claim 13, further comprising:adjusting one or more tap weights of a decision feedback equalizer orpole and gain of a continuous-time decision feedback equalizer (CT-DFE)based upon said third product.
 15. The method according to claim 13,further comprising: generating said third product by multiplying saiddifference of said first product and said second product with aplurality of previous data samples.
 16. The method according to claim15, further comprising: adjusting one or more tap weights of a decisionfeedback equalizer or pole and gain of a continuous-time decisionfeedback equalizer (CT-DFE) based upon said third product.
 17. Themethod according to claim 13, further comprising: generating a pluralityof first products by multiplying said first error sample by a pluralityof first data samples; generating a plurality of second products bymultiplying said second error sample by a plurality of second datasamples; and adjusting one or more of said gain, said pole, and said tapweight of said equalizer based upon a sum of said plurality of firstproducts and said plurality of second products.
 18. The method accordingto claim 13, wherein said one or more equalizer settings comprise tapweights of a decision feedback equalizer (DFE).
 19. The method accordingto claim 13, wherein said one or more equalizer settings comprise poleand gain of a continuous-time decision feedback equalizer (CT-DFE). 20.An apparatus comprising: an error sample generating circuit configuredto generate error samples at a plurality of phases; and an adaptationcircuit configured to generate a first product by multiplying a firsterror sample by a first coefficient, a second product by multiplying asecond error sample by a second coefficient, and a third product bymultiplying a difference of said first product and said second productby a data sample, wherein said adaptation circuit adjusts one or moreequalizer settings based upon said third product.